pg_class

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pg_class

The system catalog table pg_class catalogs tables and most everything else
that has columns or is otherwise similar to a table (also known as relations). This
includes indexes (see also pg_index), sequences,
views, composite types, and TOAST tables. Not all columns are meaningful for all relation
types.

Table 1. pg_catalog.pg_class

column

type

references

description

relname

name

Name of the table, index, view, etc.

relnamespace

oid

pg_namespace.oid

The OID of the namespace (schema) that contains this
relation

reltype

oid

pg_type.oid

The OID of the data type that corresponds to this table's row
type, if any (zero for indexes, which have no pg_type entry)

relowner

oid

pg_authid.oid

Owner of the relation

relam

oid

pg_am.oid

If this is an index, the access method used (B-tree, Bitmap, hash,
etc.)

relfilenode

oid

Name of the on-disk file of this relation; 0 if
none.

reltablespace

oid

pg_tablespace.oid

The tablespace in which this relation is stored. If zero, the
database's default tablespace is implied. (Not meaningful if the relation has no
on-disk file.)

relpages

int4

Size of the on-disk representation of this table in pages (of 32K
each). This is only an estimate used by the planner. It is updated by
VACUUM, ANALYZE, and a few DDL commands.

reltuples

float4

Number of rows in the table. This is only an estimate used by the
planner. It is updated by VACUUM, ANALYZE, and a few
DDL commands.

reltoastrelid

oid

pg_class.oid

OID of the TOAST table associated with this table,
0 if none. The TOAST table stores large attributes "out of line" in
a secondary table.

reltoastidxid

oid

pg_class.oid

For a TOAST table, the OID of its index. 0 if not
a TOAST table.

relaosegidxid

oid

Deprecated in Greenplum Database 3.4.

relaosegrelid

oid

Deprecated in Greenplum Database 3.4.

relhasindex

boolean

True if this is a table and it has (or recently had) any indexes.
This is set by CREATE INDEX, but not cleared immediately by
DROP INDEX. VACUUM will clear if it finds the
table has no indexes.

relisshared

boolean

True if this table is shared across all databases in the system.
Only certain system catalog tables are shared.

Number of user columns in the relation (system columns not
counted). There must be this many corresponding entries in pg_attribute.

relchecks

int2

Number of check constraints on the table.

reltriggers

int2

Number of triggers on the table.

relukeys

int2

Unused

relfkeys

int2

Unused

relrefs

int2

Unused

relhasoids

boolean

True if an OID is generated for each row of the relation.

relhaspkey

boolean

True if the table has (or once had) a primary key.

relhasrules

boolean

True if table has rules.

relhassubclass

boolean

True if table has (or once had) any inheritance children.

relfrozenxid

xid

All transaction IDs before this one have been replaced with a
permanent (frozen) transaction ID in this table. This is used to track whether the
table needs to be vacuumed in order to prevent transaction ID wraparound or to allow
pg_clog to be shrunk.

The value is 0
(InvalidTransactionId) if the relation is not a table or if the
table does not require vacuuming to prevent transaction ID wraparound. The table
still might require vacuuming to reclaim disk space.